Collagenous Colitis with Pseudomembranes

Abstract

Purpose: Microscopic colitis ranks highly in the differential diagnosis of chronic watery diarrhea, and is generally defined by histologic findings of colitis in a macroscopically normal mucosa. We present an unusual case of collagenous colitis with grossly abnormal endoscopic findings. A 78-year-old woman presented with intermittent watery diarrhea for two months, without abdominal pain, hematochezia, or pyrexia. Patient denied recent travel, antibiotic therapy, or sick contacts. Medications included amlodipine, benazepril, and atenolol. She was also on therapy with omeprazole for 1 year. No history of non-steroidal drug use. Physical examination was unremarkable. Stool was watery, light-colored and guaiac-negative. Blood chemistries were normal and stool studies were negative, including five assays for Clostridium difficile toxin. Colonoscopy revealed severe pancolitis with patchy exudates. Biopsies noted a thickened subepithelial collagen band in addition to mucosal erosions, inflammatory pseudomembranes, and a lymphoplasmacytic infiltrate in the lamina propria. She was initially treated empirically with vancomycin, then with mesalamine, loperamide, and bismuth subsalicylate without improvement. She subsequently responded well to a trial of prednisone 40 mg daily, followed by therapy with budesonide. She is currently in remission, on a budesonide taper. Differential diagnosis of pseudomembranous colitis is broad, but the most common causes are Clostridium difficile infection, ischemic colitis, and severe inflammatory bowel disease. Our patient had multiple negative Clostridium Difficile toxin assays and no evidence of neutrophilic infiltrate, crypt distortion or withering, or microvascular thrombi on biopsy, rendering alternate diagnoses less likely. One possible etiologic factor for microscopic colitis in this particular case is relatively recent onset of proton pump inhibitor therapy. Although usually defined by microscopic inflammation of an endoscopically normal-appearing mucosa, microscopic colitis can present with pseudomembranes in the absence of Clostridium difficile infection as previously reported in 13 cases (reviewed here). This case illustrates that collagenous colitis is not exclusively a microscopic diagnosis. Endoscopists should be aware of the atypical presentations of microscopic colitis with gross endoscopic findings.